1. Field of the Invention
The invention relates to novel polymers containing amide and ester linkages and to an improved process for preparing such polymers. More specifically the invention relates to the crystalline polyamide esters prepared from N,N'-terephthaloyldi-beta-alanine and ethylene glycol.
2. Description of the Prior Art
Polyesteramides have been known to the textile industry since as early as 1932. The first polyamide esters were prepared by the reaction of a dibasic acid or its ester with amino alcohols or a mixture of a diamine and a glycol. The resulting polymers had poor color and low crystallinity and consequently received very little attention from the textile industry.
Improved techniques consisting of the use of intermediates containing performed amide linkages which prevented side reactions yielded polymers containing regularly recurring ester and amide groups with a more crystalline structure and good color. Such techniques have been applied to polyamide ester formation from dicarboxylic acid diamides and glycols.
The formation of recurring polyamide esters from a dicarboxylic acid diamide and a glycol has typically been a three step process. The first step entails the formation of the intermediate. A dicarboxylic acid diamide is reacted with an excess stoichiometric amount of the glycol to form the diglycol ester of the acid. The excess stoichiometric amount of the glycol is required because the reaction between the dicarboxylic acid diamide takes place more readily in excess glycol. The second step entails distilling off the excess glycol from the di-glycol ester of the acid. The final step is the polymerization of the intermediate where the diglycol ester of the acid is polycondensed at elevated temperatures, typically around 230.degree.-260.degree. C., under a reduced pressure, usually less than about 5 mm Hg. Under such conditions, high molecular weight polyamide esters are yielded in approximately 30 to 60 minutes.
The above techniques have not been satisfactory for the preparation of polyamide esters from dicarboxylic acid diamide derivatives of terephthalic acid and a glycol. U.S. Pat. No. 3,420,802 reveals a polymer prepared from the dimethyl ester of terephthalic acid diamide N,N'-di-.epsilon.-caproic acid and ethylene glycol reported to have a dark color and a melting point of 213.degree.-216.degree. C. New techniques, as described in the instant invention, have been able to overcome the problems of the prior art and produce a more desirable polyamide ester from a terephthalic acid derivative and a glycol.